This invention relates to methods and apparatus for installing underwater pipelines, and particularly for connecting underwater petroleum flowlines to a subsea wellhead or other underwater facility for establishing a means to conduct produced well fluids to a reservoir or other gathering system.
Production of petroleum from offshore subsea wells has developed to the point where this activity is now in progress worldwide. After a subsea well is completed, the crude oil is conducted through a system of flowlines to a production station where it is processed and ultimately transported to an offshore loading facility or to a landbased reservoir.
Accurate placement of these flowlines so that the flowline terminal connections can be made is a difficult task when conventional pipeline laying techniques are used, especially in areas such as the North Sea where weather and water conditions are extremely hostile, and in other areas where the water depth is very great. The ends of the flowline must be laid past the subsea stations in such a manner as to form a curved or looped configuration to allow for flexibility in the flowline when the terminal connections are made. However, surface effects (wave action, wind and currents) make accurate placement of a flowline virtually impossible, and water column currents increase the liklihood of inaccuracy in this task.
Furthermore, conventional underwater pipelaying techniques require the use of specialized surface vessels which normally are very expensive, and the congestion of other flowlines, piping and ancillary equipment increases this problem. When the terminals of the flowline are pulled along the ocean floor into an alignment frame at the wellhead or other subsea station, sophisticated pulling equipment and large power requirements are needed. Still another problem is that existing techniques are not readily adaptable to both "wet" and "dry" well completion systems, that is where the wellhead connections are made in a water or air atmosphere.